Round LED Module Thermal Management - Universal Lighting ...

Application Note: EVM04
COOLING SYSTEM TEST:
ULT has characterized the thermal behavior of the round LED module and defined a location for
standardization of the temperature measurement. This measurement location is located near
the center of the module as shown in Figure 4 and is defined as T s . The temperature of the
module at this location must be maintained at or below the value outlined in the specification
sheet, 85⁰C. This requirement has been established to ensure safe operation and stated
lifetimes are achieved.
To determine from measured data if the LED is within the temperature specification, the
following relationship can be used to compare the measured thermal performance with the
reliability temperature limit either with or without a heat sink installed. This relationship applies
an adjustment to the measured Ts to compensate for the difference between the average
ambient temperature that is expected for the system and the measured ambient temperature:
T s rel test = T s meas + T a avg spec – T a meas
where:
T s rel test
is the ambient adjusted LED module solder temperature for
reliability conditions (⁰C)
T s meas
is the measured LED temperature at the location in Figure 4 (⁰C)
T a avg spec
is the expected average system ambient temperature (⁰C)
T a meas
is the measured system ambient temperature (⁰C)
The testing environment of the LED module and cooling system should simulate the application
environment as closely as possible. Air movement, power input, ambient temperature,
mechanical orientation, and other heat sources affecting the thermal performance of the LED
module need to be realistic.
The thermal environment for the typical application of linear LED modules does not have
guaranteed air movement in natural convection. Consequently, it is not recommended that
testing be performed in a thermal chamber or oven that uses forced convection or has any
significant air movement within it. Also, natural convection requires significant space to avoid
restriction of natural air movement. The module and cooling system location within the test
environment must have open area surrounding it and quiescent air.
Test multiple LED’s and ensure that the LED with the expected highest temperature is
measured.
Test until the measured temperatures stabilize at maximum values reaching steady state
temperatures.
For further assistance or ordering information please contact Universal lighting technologies @ 1-800-BALLAST or visit our website at http://www.unvlt.com/
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